The present invention relates generally to an apparatus for facilitating pre-loading of fuel rods into magazines for subsequent loading into fuel assemblies. More particularly, this invention concerns a computer-based, interactive system for assuring proper loading, by operators, of fuel rods of different enrichments in the desired pattern during manufacture of fuel assemblies for nuclear reactors.
The fuel assemblies in nuclear reactors of the type utilized in power generation generally incorporate numerous fuel rods arranged in spaced-apart relationship in a grid within a frame or "skeleton" including top and bottom nozzles or tie plates between which the fuel rods extend. Each fuel rod generally comprises a stack of enriched fuel pellets within a metal tube sealed by end plugs, which constitute the primary containment boundary of the radioactive nuclear fuel therein. All of the fuel pellets within a given fuel rod are usually of the same enrichment, but fuel rods of the same or different enrichments or multiple enrichments can be used in a particular fuel assembly depending upon the reactor type. For example, a pressurized water reactor (PWR) typically utilizes fuel assemblies with fuel rods of the same enrichment in a particular fuel assembly, while a boiling water reactor (BWR) utilizes fuel assemblies of multiple enrichments which require the fuel rods to be arranged in a particular pattern.
Proper control of the enrichments during construction of the fuel rods and then assembly of the fuel rods into the proper grid locations of the fuel assemblies, is crucial. In addition to the safety considerations involved in handling nuclear fuel, the Nuclear Regulatory Commission (NRC) has established strict quality control standards and performance requirements which must be met to start or continue operation of power reactors. Moreover, nuclear power plants are rated at particular power generation levels which can be difficult to achieve without proper enrichment control during the design, manufacture, and assembly of the fuel assemblies therein. Severe penalties can be incurred by the manufacturer if the power plant fails to generate at the rated capacity. Proper enrichment control during the manufacture of nuclear fuel assemblies is, thus, extremely important, but is complicated by the use of multiple enrichments.
It will be appreciated that proper manufacturing procedures must be implemented and followed, and that provisions must be made for verifying and documenting that fuel rods of the desired enrichments have been loaded into the desired grid locations required by the fuel assemblies.
The actual loading of fuel rods into fuel assemblies has been primarily a manual operation. The fuel rods were transported on a dolly to a position adjacent to an empty fuel assembly lying on its side on another dolly. Referring to a drawing or schematic showing the proper grid locations, the operator would pull out a fuel rod, look at the serial number thereon corresponding to its particular enrichment, compare and match that with the grid location on the schematic, and then insert the rod into the fuel assembly at the desired grid location. Also, before insertion into the fuel assembly, a label bearing the serial number thereof would be removed and applied to a "scroll" as a record of the fuel rods loaded into that fuel assembly. The scrolls would then be turned in periodically for filing or storage to serve as permanent documentation.
This manual based approach, however, is cumbersome at best, subject to operator error or fatigue, and otherwise difficult, particularly with respect to fuel assemblies with fuel rods of different and/or multiple enrichments arranged in a specific pattern. It will be appreciated that under this prior approach, numerous fuel rods and their individual grid locations must be manually identified and then inserted into the correct grid locations, which grids can be up to 17.times.17 in size, such that operator error and fatigue can be problematical. This prior approach does not provide enough early error detection and feedback to the operator for corrective action while the operator is loading the fuel assembly.
A need has thus arisen for an improved interactive fuel assembly pattern loading system which reduces operator input while providing better verification and documentation of the proper fuel rod loading pattern as the fuel assembly is being assembled.